Such dampers have been known for a long time. The range of sizes extends from the smallest dampers with diameters of less than 100 mm for automobile engines and camshafts to dampers for commercial vehicle engines of all power classes, to dampers with diameters of more than 2000 mm for large engines like ship propulsion main drives. A damper of the type described above is, for example, described in DE 198 55 419 B4.
Generally, highly viscous silicon oils are used as damping fluids. The shearing of the damping fluid and the concomitant heat generation over the period of use of the damper, leads to wear of the silicon oil especially due to the breaking up of long-chained oil molecules. This changes the damping properties of the damper until, from a certain limit onwards, the damper is not suitable any more to effect adequate damping.
This oil wear is irreversible and results in a limited life of such dampers. Through the use of chemical oil additives, the wear behavior can be improved, though not stopped.
It is therefore necessary to monitor the wear state of the oil by regular sampling and oil analysis by the damper manufacturer, if the life of the damper is shorter than that of the damped drive. As soon as the oil state exceeds a wear limit, the damper is replaced or supplied with new oil on-site.
If the dampers involved are not throw-away dampers, they are generally re-generated and prepared. This involves opening and cleaning the damper, the exchange of bearing elements, as well as the re-assembly and replenishment with oil. The bigger the damper, the more costly and involved this process becomes. With large dampers of the kind used for ship drives, dismantling, transport and reinstallation involve high costs, which can be more than the value of the damper. In addition, the plants have to be at standstill, as they cannot be operated without dampers.
It is possible to replenish the oil in the installed stated of the damper by pressing fresh oil from the outside through openings in the housing into the inside and forcing out used oil through other openings to the outside. However, the disadvantage of this procedure is that the exact filling of the damper is difficult. But such accuracy is required, since the damper must contain neither too little nor too much oil for providing the desired damping. Moreover, it is not possible to rinse out all the used oil in this manner, so that ultimately, an undefined mixture of new and used oil is generated. A certain extension of the life of the damper is possible that way. However, the condition that is achieved with such a refilling is not equivalent to that of a completely cleaned and freshly filled damper.